Update sysctl settings to match new recommendations

The recommended sysctl settings for user clusters are out-of-date, and
after some investigation we've discovered a good minimal set of
recommended defaults.  These will be updated in the documentation, but
we also want to set them in the VMs used for our CLI Behave tests so
that we use values similar to those that users will have in their
environments, so this commit adds a section to the Concourse cluster
task file to do so.
Co-authored-by: NJamie McAtamney <jmcatamney@pivotal.io>
Co-authored-by: NKalen Krempely <kkrempely@pivotal.io>

concourse/tasks/run_behave_on_ccp_cluster.yml

@@ -24,6 +24,42 @@ run:
         install_python_hacks
     '"
 
+    # setting sysctl settings
+    while read LINE; do
+        host=$(echo $LINE | awk '{ print $3 }')
+        ssh -n centos@$host "sudo bash -c '
+            # minimal settings
+            sysctl -w kernel.shmall=\`expr \$(getconf _PHYS_PAGES) / 2\`
+            sysctl -w kernel.shmmax=\`expr \$(/sbin/sysctl -n kernel.shmall) \* \$(getconf PAGE_SIZE)\`
+            sysctl -w kernel.shmmni=4096
+            sysctl -w vm.overcommit_memory=2
+            sysctl -w vm.overcommit_ratio=95
+            sysctl -w net.ipv4.ip_local_port_range=\"10000 65535\"
+            # additional settings
+            sysctl -w kernel.sem=\"500 2048000 200 40960\"
+            sysctl -w kernel.sysrq=1
+            sysctl -w kernel.core_uses_pid=1
+            sysctl -w kernel.msgmnb=65536
+            sysctl -w kernel.msgmax=65536
+            sysctl -w kernel.msgmni=2048
+            sysctl -w net.ipv4.tcp_syncookies=1
+            sysctl -w net.ipv4.conf.default.accept_source_route=0
+            sysctl -w net.ipv4.tcp_max_syn_backlog=4096
+            sysctl -w net.ipv4.conf.all.arp_filter=1
+            sysctl -w net.core.netdev_max_backlog=10000
+            sysctl -w net.core.rmem_max=2097152
+            sysctl -w net.core.wmem_max=2097152
+            sysctl -w vm.swappiness=10
+            sysctl -w vm.zone_reclaim_mode=0
+            sysctl -w vm.dirty_expire_centisecs=500
+            sysctl -w vm.dirty_writeback_centisecs=100
+            sysctl -w vm.dirty_background_ratio=0
+            sysctl -w vm.dirty_ratio=0
+            sysctl -w vm.dirty_background_bytes=1610612736
+            sysctl -w vm.dirty_bytes=4294967296
+        '"
+    done <cluster_env_files/etc_hostfile
+
     ssh -t mdw "
         source /home/gpadmin/gpdb_src/concourse/scripts/common.bash
         install_python_requirements_on_multi_host /home/gpadmin/gpdb_src/gpMgmt/requirements-dev.txt